System for controlling a rotary device

ABSTRACT

A system for controlling a rotatable device, the system comprising a controller and a rotary device, which has a stator and rotor, wherein the controller is connected to the rotary device to control rotation of the rotary device, and wherein the controller is adapted to periodically energizes at least one energizing coil of the device to create a magnetic field of a polarity which induces the rotor to rotate in a single direction and wherein the controller is switched off so as to de-energize the energizing coil when other forces, being forces other than those resulting from the energized energizing coil, produce a resultant force which induces rotation of the rotor in the single direction.

FIELD OF THE INVENTION

The present invention relates to motors which are used for generating atorque and generators which are used for generating electricity.

BACKGROUND OF THE INVENTION

A typical electric motor consists of a stator and rotor.

The operation of an electric motor is based on the principal that anelectric current through a conductor produces a magnetic field, thedirection of current in an electro-magnetic such as a coil of wiredetermines the location of the magnets poles and like magnetic polesrepel and opposite poles attract.

The stator which is typically called the field structure establishes aconstant magnetic field in the motor.

Typically the magnetic field is established by permanent magnets whichare called field magnets and located at equally spaced intervals aroundthe rotor.

The rotor or armature typically consists of a series of equally spacedcoils which are able to be energised to produce a magnetic field andthus north or south poles.

By keeping the coils energised the interacting magnetic fields of therotor and the stator produce rotation of the rotor.

To ensure that rotation occurs in a single direction a commutator istypically connected to the windings of the coils of the rotor so as tochange the direction of the current applied to the coils.

If the direction of the current was not reversed the rotor would rotatein one direction and then reverse its direction before a full cycle ofrotation could be completed.

The above description typifies a DC motor. AC motors do not havecommutators because alternating current reverses its directionindependently.

For a typical AC motor such as an induction motor the rotor has nodirect connection to the external source of electricity. Alternatingcurrent flows around field coils in the stator and produces a rotatingmagnetic field. This rotating magnetic field induces an electric currentin the rotor resulting in another magnetic field.

This induced magnetic field from the rotor interacts with the magneticfield from the stator causing the rotor to turn.

An electric generator is effectively the reverse of an electric motor.Instead of supplying electricity to coils of either the stator or rotor,the rotor or armature is rotated by physical forces produced by a primemover.

In effect a generator changes mechanical energy into electrical energy.

SUMMARY OF THE INVENTION

The present invention is aimed at providing an improved rotary devicewhich operates with improved efficiency compared to conventional rotarydevices.

The present invention is also concerned with providing a system forcontrolling a rotary device which is able to generate electrical and/ormechanical energy.

According to the present invention there is provided a system forcontrolling a rotary device, the system comprising a controller and arotary device, which has a stator and rotor, wherein the controller isconnected to the rotary device to control rotation of the rotary device,and wherein the controller is adapted to periodically energise at leastone energising coil of the device to create a magnetic field of apolarity which induces the rotor to rotate in a single direction andwherein the controller is switched off so as to de-energise theenergising coil when other forces, being forces other than thoseresulting from the energised energising coil produce a resultant forcewhich induces rotation of the rotor in the single direction.

Preferably the controller is adapted to energise the energising coil fora period during which the resultant force from the other forces acts torotate the rotor in the opposite direction, whereby the force applied bythe energising coil overcomes (is greater than) the resultant force.

The controller is preferably adapted to switch off to de-energise theenergising coil before the resultant force is zero.

The controller preferably is adapted to switch off to de-energise theenergising coil for a period before the resultant force is zero, and toallow back EMF induced by other forces to urge the rotor to rotate inthe single direction before the resultant force is zero.

Preferably the resultant force excludes forces arising from back EMF.

The energising coil may be adapted to be energised by the controllerthrough a predetermined angle of a complete revolution of the rotor.

Alternatively the energising coil is adapted to be energised by thecontroller for a predetermined period of time for each revolution of themotor.

Preferably the/each energising coil is energised more than once during asingle revolution (cycle) of the rotor.

The/each or at least one energising coil may be energised each time theresultant force applies a force to the rotor in the opposite direction.

The/each or at least one energising coil may be energised by a periodicpulse applied by the controller.

The periodic pulses are preferably all of the same sign.

The/each or selected ones of the energising coils are energised wheneverthe resultant force is in the opposite direction and then for a periodless than the period during which the resultant force changes from zeroto a maximum and back to zero.

According to one embodiment the stator has the at least one energisingcoil.

The rotor may have at least one magnetic field generating means which isable to generate a magnetic field which interacts with the magneticfield generated by the/each energising coil when energised, to apply aforce to rotate the rotor in one direction.

The/each energising coil preferably includes a magnetic interactionmeans which is adapted to either repel or attract the magnetic fieldgenerating means.

According to another embodiment the magnetic interaction means isadapted to attract the magnetic field generating means.

The magnetic interaction means may comprise a ferrous body or body ofanother substance which is attractable to a magnetised body.

The magnetic field generating means may be a permanent magnet.

The magnetic interaction means may be an iron core or a permanentmagnet.

Preferably the magnetic field generating means comprises a permanentmagnet, or member attractable to a magnetised body.

The stator preferably comprises a plurality of energising coils evenlyspaced around the rotor.

Each energising coil is preferably an electromagnet.

Preferably the or each energising coil includes the magnetic interactionmeans through its coil.

Preferably the rotor comprises a plurality of evenly spaced magneticfield generating means.

According to one embodiment the rotor comprises a plurality of evenlyspaced permanent magnets.

The evenly spaced permanent magnets may all be of the same polarity.

The evenly spaced magnetic field generating means may be energisablecoils simulating magnets.

Preferably the poles of the magnetic field generating means are all thesame.

The magnetic poles produced by energised energising coils may be thesame as that for the magnetic field generating means.

According to an alternative embodiment an alternating pattern of polesfor the energising coils is provided.

According to another embodiment an alternating pattern of permanentmagnets is provided for the rotor.

According to a further embodiment of the present invention the statorhas a plurality of magnetic flux generating means.

The magnetic field generating means for the stator may be permanentmagnets.

Preferably the rotor comprises a plurality of energising coils and acommutator.

The rotor may be an armature and the stator may be a field winding.

Preferably the rotor magnetic field generating means is energised by anexternal power supply being DC or AC current.

The stator magnetic interaction means may be energised by coilsoperating on AC or DC current.

According to one embodiment the stator includes at least one inductioncoil which is adapted to have a current induced therein by the magneticfield generating means of the rotor.

The/each induction coil may be separate from the/each energising coil.

The/each induction coil may also be the energising coil.

The/each energising coil may be adapted to be connected to an outputcircuit whereby current induced in the/each energising coil is output tothe output circuit.

It is preferred that switching circuitry is adapted to rectify currentinduced in the induction coils.

It is preferred that the rectifying occurs just before the or eachenergising coil is energised by the power supply.

Preferably current output to the output circuit is adapted to be used torun an electric device.

The controller preferably comprises a switching circuit which is adaptedto connect the/each energising coil to an output circuit when no currentis generated to energise the energising coil.

Preferably the controller provides a switching circuit.

The controller may be a rotary switch.

The rotary switch may have at least one contact which is aligned withthe/each magnetic field generating means.

Preferably the rotary switch has at least one contact aligned with thepermanent magnets of the rotor.

The rotary switch may have the same number of contacts as the number ofMagnetic field generating means; being magnets in their preferred form.

The/each contact may have a width that varies with vertical height.

The rotary switch preferably comprises adjustable brushes which are ableto be moved vertically.

The contacts preferably taper in width from a top end to a bottom endthereof.

The rotary switch and rotor may be located on coaxial central axis.

The rotary switch and rotor may be mounted on a common axial.

Preferably the rotor switch is mounted in a separate chamber from therotor.

According to one embodiment each energising coil is adapted to repel anadjacent magnetic field generating means when energised.

Each energising coil may be adapted to be energised by back EMF only fora predetermined period of each cycle.

The predetermined period preferably occurs after current to theenergising coil is switched off.

According to a further embodiment the/each energising coil is adapted toattract the magnetic field generating means of the rotor.

The present invention contemplates a number of variations to thecomponents making up the systems described above. For example thecurrent, voltage, magnetic field generated, the number of poles ofmagnets for the rotor/stator may all vary and accordingly will effectthe timing of switching of energising coils.

The rotary device may have a greater number of magnetic poles generatedon the stator/field winding than in the rotor/armature or vice versa.

According to one embodiment the number of poles on both of these are thesame.

It is preferred that the switching of the energising coils which iscontrolled by the controller is adapted to maximise the influence ofback EMF produced.

It is preferred that the energising coils are effectively provided witha pulsed electric current of minimum duration, which duration is enoughto maintain rotation of the rotor and produce a desired output of torqueor current.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described byway of example only with reference to the accompanying drawings inwhich:

FIG. 1 shows a cross-sectional front view of a rotary device an acontrol therefore in accordance with a first embodiment of theinvention;

FIG. 2 shows a top view of the controller shown in FIG. 1,

FIG. 3 shows a side view of the controller shown in FIG. 1;

FIG. 4a shows a schematic view of a system for controlling rotary devicein accordance with the first embodiment of the present invention;

FIG. 4b shows a schematic view of the rotary device shown in FIG. 4a;

FIG. 5 shows a graphical representation of force versus angular positionof permanent magnet M1 of the system shown in FIG. 4a;

FIG. 6 shows a series of four graphs of input current versus angularmovement of each permanent magnet of the system shown in FIG. 4a;

FIG. 7 shows a graphical representation of input voltage versus inputcurrent for each coil of the rotary device shown in the system of FIG.4a;

FIG. 8 shows a schematic diagram of variation of natural magneticattraction versus angular displacement of a rotor having a singlepermanent magnet and a stator having a single energising coil, inaccordance with a second embodiment of the present invention;

FIG. 9 shows a graphical representation of magnetic field versus angulardisplacement in accordance with the second embodiment of the presentinvention;

FIG. 10 shows a graphical representation of induced induction versusangular displacement of the permanent magnet in accordance with thesecond embodiment of the present invention; and

FIG. 11 shows a further graphical representation of induced inductionelectro-magnetic force versus angular displacement of the permanentmagnet in accordance with the second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIG. 4a according to the first embodiment of the invention asystem is provided consisting of a rotor 11 having four permanentmagnets M1, M2, M3 M4 which are evenly spaced at 90° with respect toeach other.

The system includes a stator 12 consisting of three electromagnetenergising coils A, B, C which are spaced 120° apart from each other.

Each coil A, B, C is connected in circuit with a power supply of 54volts and a switch RS1, RS2, RS3.

Each of the contacts RS1, RS2, RS3 are part of a rotary switch 13 havingcontacts 14, 15, 16, 17 which are spaced apart at 90° with respect to anadjacent contact.

The rotary switch 13 is provided with contact brushes 18, 19 and ismounted on an axle 20 which is the same or common with the axle of therotor 11.

Each of the contacts 14, 15, 16, 17 is specially configured with atrapezoidal shape, with the two non-parallel sides consisting of astraight side 21, and a tapered side 22 which tapers outwardly from topside 23 to bottom side 24.

The result is that each contact increases in a width moving from the topside to the bottom side 24.

The brush 18 is able to be moved vertically relative to the contacts 14,15, 16, 17 while the brush 19 is in constant contact with the base.

Although FIG. 1 only shows the rotary switch 13 having a single seriesof four contacts 14, 15, 16, 17, for the three coil stator shown in FIG.4a there would in fact be preferably three contact discs on the axle 20.

Each contact disc would have contacts for a respective one of the coilsA, B, C, but each brush for the other discs would be offset by 30° and60° respectively.

A description of the operation of the system shown in FIGS. 1 to 4 awill now be set forth below.

If it is assumed that the magnets M1, M2, M3 M4 are initially aligned asshown in FIG. 4a with magnet M1 opposite one end of coil A, coil A isenergised whenever one of the magnets M1 to M4 is aligned opposite itand for a predetermined time after the permanent magnet has passed it.

As shown in FIG. 6 coil A is energised by contact RS1 providing anelectrical connection through the rotary switch 13.

This occurs by one of the contacts 14 to 17 being aligned in contactwith brush 18. At this time current is applied from the power source VAand continues to be applied until the brush 18 is no longer in contactwith one of the contacts 14 to 17.

For the three coil/four pole arrangement of the first embodiment it ispreferred that the brushes are moved to a vertical position where thewidth of each contact is sufficient for each of the switches RS1, RS2and RS3 to be closed for 12° 51′, 50″ of the rotation of the rotor 11.After this time the switches RS1 to RS3 are open and no more current isdelivered to any one of the coils A to C. When the current to each ofthe coils is switched off a back EMF is induced in each of the coils Ato C and thin back EMF represented by item Z results in current beingmaintained in each of the coils for an additional small period of tireafter the contacts RS1 to RS3 are opened.

By switching the coils A to C in the above manner the rotor 11 can beinduced to rotate with a lower amount of input current to the statorthan would be required if current was delivered constantly to the coilsA to C.

Table 1 below shows the resultant force on the rotor 13 for angularpositions of the magnets M1 to M4 for angular displacements of magnetfrom 5° to 30°.

TABLE 1 M1  5° CC 10° CC 15° CC 20° CC 25° CC 30° CC M2 25° CW 20 CW 15CW 10 CW  5° CW  0° M3 55° CW 50° CW 45° CW 40° CW 35° CW 30° CW N4 35°CW 40 CC 45° CC 50° CC 55 CC 60 RF CC CC 0 CW CW  0

As shown when the magnets of the rotor 13 are rotated 50 at a time theresultant force on the rotor changes from a counter clockwise force from5° to 15° to a clockwise force from 15° to 30°.

At 0°, 15° and 30° the resultant force on the rotor is 0 so that if thepermanent magnets of the rotor were aligned in any of these orientationsthere would be no resultant force to urge the rotor either clockwise oranti clockwise.

As shown in FIG. 5 a plot of magnitude of resultant force applied to therotor against angular displacement of the rotor shows a sinusoidal curvehaving a cycle of 30°.

For a full 360° rotation of the rotor the rotor would experience 12cycles of variation in resultant force.

What Table 1 and FIG. 5 shows is that unless an additional force isapplied to rotate the rotor clockwise or anticlockwise the rotor willnot be able to spin continuously in either direction.

If it is assumed that it is desired to rotate the rotor clockwise, thenthe force must overcome the counterclockwise resultant force whichoccurs from 0 to 15°, 30° to 45°, 60° to 75° etc through the whole 360°rotation of the rotor.

Because each of the coils A to C has an iron core even when the coilsare unenergised the natural magnetic attraction occurring between eachmagnet and the iron cores results in each magnet M1 to M4 attempting tomove in a direction to the closest iron core.

Whenever a magnet is opposite an iron core the magnetic attraction isgreatest and there is no force applied by that magnet to move the rotoreither clockwise or counterclockwise. Likewise when a magnet ispositioned midway between adjacent iron cores, there is also a resultantforce of 0 which translates to no resultant force being applied to therotor to rotate it in either direction by that magnet.

As shown in FIG. 5 and Table 1 if magnet M1 is moved clockwise 5° thereis a natural attraction between the magnet M1 and iron core of coil A topull the magnet M1 in a counter clockwise direction. If the resultantforces applied by the other magnets were sufficient to overcome theattraction between permanent magnet M1 and the iron core of coil A therotor would still manage to move clockwise.

However as shown in Table 1 the angular position of the other magnets M2to M4 results in an overall counter clockwise resultant force

To overcome the resultant force it is necessary to produce a pole X atcoil A of like polarity to magnet M1 and thus repel M1 away from coil A.

As shown in FIG. 5 the strength of the magnetic repelling action betweencoil A and M1 must be sufficient to overcome the resultant force urgingthe rotor counter clockwise.

A current could be applied to the coil A for an angular displacement of15° of magnet M1, but it is preferred that coil A be energised only for12°, 51′, 50″ angular displacement of magnet M1. By applying current tocoil A for this period of angular displacement a minimum amount ofcurrent is applied to coil A in order to overcome the resultant forcecounter clockwise which occurs for 0° to 15° of angular displacement ofmagnet M1.

Although current to coil A can be applied for longer than this period ithas been discovered that by applying current for this period a back EMFis induced in coil A which adds to the repulsive force applied to magnetM1 by coil A.

Every time one of the magnets M1 to M4 is aligned at 0° with coil A coilA is energised for 12°, 51′, 50″ of angular displacement of that magnet.Thus as shown in FIG. 6 current ends up being applied to coil A at 0° to12°, 51′, 50″, 90° to 102°, 51′, 50″, 180° to 192° , 51′, 50″ and 270°to 282°, 51′, 50″.

A similar switching pattern is applied to coils B and C. For examplecoil B is energised when magnet M2 has moved 30° to when it has moved42°, 51′, 50″ and likewise coil C is energised when magnet M3 has moved60° to 72°, 51′, 50″.

It is preferred that the rotor has a diameter of 230 mm and that eachcoil has a resistance of 6.8 ohms.

FIG. 7 shows a graphical representation of input voltage versus inputcurrent for a coil resistance of 6.8 ohms and for a four pole rotorwhich is 230 mm in diameter.

The exact timing sequence for switching coils on and off will varydepending on the parameters of the rotary device and the controller.

Accordingly by varying the input voltage, coil resistance and overallimpedance of the input circuit for each coil the duration during which acoil must be turned on will change.

In fact there are many factors which can change the timing sequence ofswitching on the coils and some of these are summarised below.

The Stator

The variables include the choice of material used in constructing thestator iron core, the number of stator iron cores and their positioningas well as the physical size, section area and shape of the stator ironcores.

Rotor

The physical size and magnetic strength and shape of the polarisedpermanent magnetic body as contained in the rotor, the number ofpolarised permanent magnetised bodies being contained in the rotor, thepositioning and spacing of the same, the use of all like polarities ofpermanent magnetic bodies or the use of alternating polarities for thepermanent magnetic bodies.

Stator Coil

The physical size of the coils being positioned onto the stator ironcore(s), the type of wire used to wind the coil(s) such as copper,silver, aluminum or others. The shape and section areas of the windingwire, such as round, square, triangular, rectangular and others; thenumber of turns and layers wound onto the coil and consequent ohmsresistance; the method of winding onto a coil holder, single winding,double winding, double winding same direction, double winding oppositedirection, left to right or vice versa, interwoven winding, whether theabove examples would be wound onto a single coil holder.

Speed of Rotor

This can be controlled by the length of the directed (input) DC current(on and cut off period) and/or the control of the supply voltage used tosupply the stator coil(s).

Other variations that may be made to the system include the following:

a. The coils can be connected in series, parallel, or series parallel.

b. It is only when the north/south arrangements of the permanent magnetsare used in the rotor that even numbers of permanent magnets arenecessary, but not necessarily even numbers of pairs of stator coilspositioned in the stator. Furthermore the direction DC current Suppliedto the stator coils in the north south arrangement above must besynchronised, meaning that the magnetic field as needed in the statorcoil(s) must be of corresponding polarity to the stator coil(s), ironcore end, which faces the permanent magnets.

c. When using permanent magnets which are all of the same polarity, thenany number of permanent magnets in the rotor may be used providing thereis sufficient room to contain them at even spacings on the rotor.

d. The spacings between the permanent magnets must be exact, if tooclose to each other the directed DC current will become less effective,if too far apart the full potential will not be obtained.

e. It is possible to have various combinations of permanent magnet andstator coil iron cores similar but not restricted to the following:

i. Three magnets in the rotor, one to three stator coils can be used.

ii. Five permanent magnets in the rotor, one to five stator coils can beused.

iii. Nine permanent magnets in the rotor one to three or nine statorcoils can be used.

iv. The output varies with each combination.

v. Regardless of the rotor containing even or uneven numbers ofpermanent magnets the stator can operate with only one stator coil andstator iron core and still be highly efficient but with reduced totaloutput.

f. The stator and rotor should be made from non magnetic materials likewood, plastic, bronze and similar non-magnetic materials.

Although switching is performed in its preferred form by a mechanicalrotary switch, it can also be performed by solid state electronics orother switching devices.

The length of the on period for each coil is the physical length ratio.When the brushes are in contact with the conductive part of the rotaryswitch and the non-conductive part.

This ratio is referred as the frequency or number of ratios in onesecond.

The output produced by the rotary device can be mechanical andelectrical at the same time or may be mainly electrical or mainlymechanical. The reason for this will be explained with reference to thesecond embodiment in which it is assumed the stator has a singleenergising coil with an iron core and the rotor has a single permanentmagnet.

When the rotors permanent magnet is rotated very slowly by hand in theclockwise direction it is possible to determine the point where thenatural magnetic attraction between the rotors permanent magnet and thestators iron core occurs.

When the leading edge of the permanent magnet has reached point A asshown in FIG. 8, the natural magnetic attraction begins and increasesexponentially until the centre of the permanent magnet is aligned atpoint B opposite the iron core 30.

If the permanent magnet is rotated away from point B the NMA will be ata maximum point at point B and then decrease from maximum exponentiallyuntil the trailing edge of the permanent magnet has reached point C andthen ceases.

When the rotor is moved clockwise at a constant speed and anoscilloscope is connected to the stator coil it is possible to observethe movement of the permanent magnetic between point A and point B andthen between point B and C as shown in FIG. 9.

An induced induction curve is then apparent on the oscilloscope and thisinduced induction produces a sine wave curve 31. Furthermore the inducedinduction between point A to point B is a negative going inducedinduction in this instance and the induced induction between point B andpoint C is a positive going induced induction in this instant.

It is also noted that the negative going and positive going inducedinduction curves are exactly the same but opposite to each other.

When the permanent magnet begins to induce a negative going induction inthe stator coil at 0° of the sine wave curve 31, the induction inducedis then at 0. At 90° degrees of the sine wave curve the inducedinduction is at a maximum and then goes back to 0 when the permanentmagnet is aligned with point B, or at 180° of the sine wave curve, whenthe permanent magnet starts to move away from its alignment with point Bor is at 180° of the sine wave curve.

When the permanent magnets start to move away from its alignment withpoint B and is moving towards point C the now positive going inducedinduction is first at 0 at 180° of the sine wave curve, then at amaximum of 270° of the sine wave curve and then back to 0 at 360° of thesine wave curve.

It should be noted that 0° and 360° a of the sine wave curve are notnecessarily the same as point A for 0° and point C for 360° of the sinewave curve.

Points A and C are determined by the strength of the rotors permanentmagnet and the section area and/or shape of the stator iron core.

The negative going induced induction between 0° and 180° of the sinewave curve produces an electro-magnetic force in the stator coil andiron core of opposite polarity.

The iron core end facing the rotor is of opposite polarity than thepermanent magnet in this instance, as shown in FIG. 10.

The positive going induced induction between 180° and 360° of the sinewave curve produces an electro-magnetic force in the stator coil andiron core of the same polarity in the iron core end facing the rotor,being of the same polarity as the permanent magnet in this instance.

When the permanent magnet reaches point A the natural magneticattraction between the permanent magnet and the stator iron core is atis minimum and starts to move toward point B. When the induced inductionthen also starts to occur at 0° of the sine wave curve, being somewherebetween point A and point B, the natural magnetic attraction has alreadyincreased.

When the permanent magnet is at 0° of the sine wave curve and is movingtowards point B or 180° of the sine wave curve, the negative goinginduced induction in the stator coil is producing an electro-magneticforce (field) in the stator iron core with the iron core end facing therotor being of an opposite polarity than the permanent magnet and is atzero effect at 0° of the sine wave curve, than at maximum effect at 90°of the sine wave curve and then back to zero effect at 180° of the sinewave curve.

The permanent magnet is then aligned at point B. There the magneticattraction force is proportional with the distance and this increasesexponentially when moving from A towards point B. There the stator ironcore is fixed and stationary at point B. Accordingly it will be thepermanent magnet that moves towards point B.

As an example if the stator iron core was also a polarised permanentmagnetic body of the same strength but of opposite polarity to thepermanent magnet, the magnetic attraction force would be at least fourtimes greater because of the distance factor as explained earlier.

Furthermore, this would also occur because of the doubling of themagnetic force between the magnetic north and south arrangement. Itfollows therefore that the magnetic attraction between the permanentmagnet and the iron core end facing the rotor increases dramaticallywhen the induced induction in the stator coil produces anelectro-magnetic force of the opposite polarity at the stator iron coreend facing the rotor as described above.

The increase follows the sine wave curve starting from 0° to 90° of thesine wave and the above effect decreases form 90° back to 180° of thesine wave curve.

A combination curve of the natural magnetic attraction and the inducedinduction in the stator coil, producing an electro-magnetic force at thestator iron coil end facing the rotor of opposite polarity 33 is shownin FIG. 10 from 0° to 180°. For 180° to 360° the stator iron coil androtor of like polarities 34 are shown.

When the permanent magnet is aligned at point B and a direct current issupplied to the stator coil for only a short period starting at point Bthen the DC current is applied only long enough to overcome the naturalmagnetic attraction between permanent magnet and the stator's iron coreend facing the rotor. The directed DC current as supplied to the statorcoil is producing a like-polarity at the iron core end facing the rotorand thus is repelling the permanent magnet away from point B towardspoint C.

The natural magnetic attraction has thus changed to natural magneticrepulsion due to the like-polarity of the stator iron core end facingthe rotor.

The length of the “on” period has to be sufficient to overcome thenatural magnetic attraction and could be as long as until the trailingedge reaches point C where the natural magnetic attraction ceases.However there the positive going induced induction in the stator coil asproduced by the permanent magnet produces an electro-magnetic force inthe stator or iron core end facing the rotor, producing a like polarityas the permanent magnet starting at 180° of the sine wave curve or pointB and zero at that instant. At 270° of the sine wave curve, it is at amaximum and then ends up at zero at 360° of the sine wave curve. Inother words at 270° of the sine wave the force is at maximum repulsionand there is induced induction in the stator coil depending on the speedof the rotor. The effect of variation on the speed of the rotor is shownby curves 35 in FIG. 11.

As shown in FIG. 11 regardless of the speed of the rotor the inducedinduction in the stator coil is at a maximum at 270° of the sine wavecurve.

The on period can be brought back to the point where the inducedinduction is great enough to carry the electro-magnetic repulsionthrough to 360° of the sine wave curve and beyond point C. Therefore thegreater the rotor speed the shorter the on period of the input DCcurrent has tube due to the high induced induction in the stator coil asexplained earlier. When the “on” period is switched off it is called the“cut-off” point. From the cut-off point to 360° of the sine wave curvethe repulsion is produced by back EMF the induced induction in thestator coil as previously explained.

During the on period, the magnetic repulsion force produced between thestator iron core at point B and the permanent magnet can be viewed as acombined repulsion force. Some of this force is produced by naturalmagnetic repulsion of the permanent magnet and some by the input DCcurrent as supplied to the stator coil. Therefore if the inducedmagnetic force as produced by the input DC current in the stator coil ismade equal to that of the permanent magnet with the same polarity, thenhalf of this repulsion force between the on period and the cut-offpoint, in this instance, is from the natural magnetic repulsion of thepermanent magnet as a reaction to the induced magnetic force as suppliedby the input DC current to the stator coil.

The input DC current as supplied to the stator coil produces themagnetic repulsion force and is the only outside input to the overallsystem for total movement between point A and point C.

The total input can be summarised as:

a. The combined natural magnetic attraction and the electro-magneticforce as produced by the induced induction in the stator coil betweenpoint A to point B.

b. The combined magnetic repulsion force between the permanent magnetand the stator iron core facing the rotor during the on period and thecut-off point.

c. The electro-magnetic repulsion (see induced induction as explainedearlier) between the cut-off point and point C.

d. The electro-magnetic repulsion produced by the back EMF asrepresented by shaded portion 36 of FIG. 11.

According to another embodiment of the present invention the stator hastwo coils positioned at 180° with respect to each other and the rotorhas three permanent magnets spaced at 120° apart.

As set out in Table 2 below from 0 to 30° the resultant force urges therotor counter clockwise. At 30° the resultant force is 0 and from 30° to90° the resultant force is clockwise. From 90° to 120° the resultantforce is counter clockwise. This completes a full cycle which isrepeated three times throughout a 360° rotation of the rotor.

TABLE 2 M1  5° C. 10° CC 15° CC 20° CC 25° CC 30° CC M2 55 CW 50 CW 45CW 40 CW 35 CW 30 CW M3 65 CC 70 CC 75 CC 80 CC 85 CC 90 RF CC CC CC CCCC  0

With the above configuration of poles and coils if it is desired to movethe rotor clockwise, current would need to be supplied to the coils ofthe stator to overcome the counter clockwise force whenever this iscounter clockwise, but as explained previously, current does not need tobe supplied to the coil to energise the coil for the full period duringwhich the resultant force is counter clockwise.

For convenience and ease of explanation the above embodiments have beenrestricted to permanent magnets on the rotor and coils on the statorHowever the basic concept behind the invention does not change if thepermanent magnets are replaced by coils which are energised to producethe appropriate magnetic poles.

Similarly for an AC rotary device a rotating magnetic field generated bythe stator winding or by the rotor/armature winding could similarly beswitched to reduce the amount of current required to maintain rotationof the motor in one direction and to maximise the influence of back EMFon maintaining rotation of the motor in a single direction.

The above principles also apply to generators where coils are energisedto produce a magnetic field. In such a situation the coils are switchedon for a time sufficient to maintain rotation in the single directionand to maximise the influence of back EMF which tends to maintainrotation of the rotor/armature in a single direction.

By using the above concept it is possible to produce an output which canbe both mechanical and electrical at the same time. Current generated inthe stator coil windings can be used as an output and likewise thetorque generated by the rotor can be used to supply a mechanical output.Likewise only one or the other form of output may be utilised.

What is claimed is:
 1. A system for controlling a rotatable device, thesystem comprising a controller and a rotary device, which has a statorand rotor, wherein the controller is connected to the rotary device tocontrol rotation of the rotary device, and, wherein the controller isadapted to periodically energise at least one energising coil of thedevice to create a magnetic field of a polarity which induces the rotorto rotate in a single direction and wherein the controller is switchedoff so as to de-energise the energising coil, and any other energisingcoils, when other forces, being forces other than those resulting fromthe energised energising coil, and any other energising coils, produce aresultant force which induces rotation of the rotor in the singledirection.
 2. The system as claimed in claim 1 wherein the controller isadapted to energise the at least one energising coil for a period duringwhich the resultant force from the other forces acts to rotate the rotorin the opposite direction, whereby the force applied by the at least oneenergising coil is greater than the resultant force.
 3. The system asclaimed in claim 2 wherein the controller is adapted to switch off inputcurrent to the energising coil before the resultant force is zero. 4.The system an claimed in claim 3 wherein the controller is adapted toswitch off the at least one energising coil for a period before theresultant force is zero and to allow back EMF to urge the rotor torotate in the single direction before the resultant force is zero. 5.The system as claimed in claim 4 wherein the at least one energisingcoil is adapted to be energised by the controller through one or morepredetermined angles of a complete revolution of the motor.
 6. Thesystem as claimed in claim 4 wherein the energising coil is adapted tobe energised by the controller for one or more predetermined periods oftime for each revolution of the rotor.
 7. The system as claimed in claim5 wherein the at least one energising coil is adapted to be energisedmore than once during a single revolution of the rotor.
 8. The system asclaimed in claim 7 wherein at least one of the energising coils isenergised each time the resultant force applies a force to the rotor inthe opposite direction.
 9. The system as claimed in claim 8 wherein atleast one energising coil is energised by a periodic pulse applied bythe controller.
 10. The system as claimed in claim 9 wherein theperiodic pulses are all of the same sign.
 11. The system as claimed inclaim 10 wherein the at least one of the coils is energised whenever theresultant force is in the opposite direction to the single direction andthen for a period less than the predetermined period during which theresultant force changes from zero to a maximum.
 12. The system asclaimed in claim 11 wherein the rotor has at least one magnetic fieldgenerating means which is able to generate a magnetic field whichinteracts with the magnetic field generated by the energising coil whenenergised to apply a force to rotate to the rotor in one direction. 13.The system as claimed in claim 12 wherein the energising coil includes amagnetic interaction means which is adapted to either repel or attractthe magnetic field generating means.
 14. The system as claimed in claim13 wherein the magnetic interaction means comprises an iron core of atleast one of the energising coils and the magnetic field generatingmeans comprises at least one permanent magnet.
 15. The system as claimedin claim 14 including a switching circuit which is adapted to switch offthe controller and connect the energising coils to an output wherebyincluded current in the energising coils can be used.
 16. The system asclaimed in claim 15 wherein the controller comprises a rotary switch.17. The system as claimed in claim 16 wherein the rotary switchcomprises contacts having a cross-sectional width which varies withheight.
 18. The system as claimed in claim 6 wherein the at least oneenergising coil is adapted to be energised more than once during asingle revolution of the rotor.